Radio navigation aids. Aids to final approach and landing. ILS.

RADIO NAVIGATION AIDS - VOR/DME.

Apart from taking their bearings from the stars, how do pilots navigate? The answer, of course, is in the use of radio navigation aids. There are a variety of different types of radio navigation aids but here we shall discuss VOR and DME only.

VOR and DME are often located at the same site. They operate on VHF and UHF respectively and, as a consequence, are not affected by static or other interferences. The maximum range of VOR is about 200 nautical miles. By flying VOR the pilot ensures he is flying directly to the station. Also by measuring his radials from more than one VOR station, a pilot can check his position.

The function of DME, which is short for Distance Measuring Equipment, is, as its title describes, to measure distance. The DME measures, electronically, the time it takes for a signal, transmitted from an aircraft interrogator, to reach the ground base station transponder, and return. This elapsed time is converted to miles and appears on a digital indicator on the flight deck. The indicator actually seems to rapidly count the number of miles between the aircraft and the station giving the pilot a continuous digital reading of how far he is from, or to, a station.

With the many VOR/DME stations along his route, a pilot can make good his desired track; is constantly aware of his distance to or from a DME station; or, by using two VOR radials, establish his exact position.

RADIO NAVIGATION AIDS. AIDS TO FINAL APPROACH AND LANDING. ILS.

By using VOR and DME a pilot knows he is on the correct course and he also knows his distance to the VOR/DME station. With this equipment the aircraft will be brought directly over the VOR/DME station from which point an approach can usually be made.

In poor weather conditions, however, a more precise landing aid is used. The ILS is the ICAO approved international standard electronic landing aid and is installed at nearly all major aerodromes.

The ILS functions with equipment in the aircraft and on the ground. On the aerodrome a localizer transmits a narrow radio beam and another transmitter provides a glide path at a fixed angle of approach. On the aircraft instrument panel an ILS indicator shows the aircraft's position in relation to the centre line of the runway and to the glide path. The ILS can, therefore, guide the aircraft along the proper approach path down to a point where the pilot must be able to see the ground and be able to continue his approach to land. If he cannot see the ground at this point, he must decide to overshoot, go around and try to land again.

In addition to the ILS localizer and glide path, an ILS installation also comprises two or three fan markers: one called the outer marker Is situated from four to six miles from the threshold of the runway; a second called the middle marker is situated approximately half a mile from the threshold of the runway, and the third, called the inner marker (installed only when required) is about 1,000 feet from the threshold of the runway. These fan markers alert the pilot of his passing over these markers by causing a light on the aircraft instrument panel to flash on and off while he is over each marker.

Дата добавления: 2015-10-30